Conventional galvanic dry cells for use in flashlights, toys or other sundry devices generally comprise a cylindrical container, such as a zinc anode can, with a depolarizer mix filling most of the container and having a carbon rod in the center which functions as the current collector for the depolarizer mix. The cells are generally provided with a subseal or inner seal which may comprise a layer of solidified molten wax or asphalt poured over a paper washer located just above the cathode depolarizer mix. Alternatively, the cells may be provided with a subseal comprising a wax bead sealed plastic washer disposed over the depolarizer mix. These subseals are reasonably effective in sealing off the depolarizer mix on shelf storage but if for any reason the cell develops excessive gas, the subseal may crack or rupture thereby enabling the gas to escape past or through a gas permeable outer seal. Once this occurs, the life span of the cell is potentially shortened by moisture loss and oxygen ingress.
Other types of galvanic cells may generate large quantities of gas under certain conditions during use. Since this type of cell is required to be tightly sealed at all times in order to prevent loss of electrolyte by leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible expolsion of the cell if not properly vented. If a vent valve is employed, it must be resealable in order to avoid drying out of the electrolyte over the life of the cell and to prevent ingress of oxygen from the atmosphere which can cause wasteful corrosion of the anode.
In the past, several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member such as a flat rubber gasket which is biased into sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily break the seal and allow the gas to escape through the vent orifice.
Another type of resealable pressure relief vent valve that has been tried is that disclosed and claimed in U.S. Pat. No. 3,293,081 issued to J. L. S. Daley on Dec. 20, 1966. This resealable vent valve basically includes an annular seal gasket such as an O-ring which is maintained in sealing position around the periphery of the vent orifice by means of an arc shaped resilient member or spring. The resilient member or spring is designed to yield and permit radial movement of the seal gasket so as to momentarily break the seal and allow the passage of gas through the vent orifice when a predetermined high internal gas pressure is reached in the cell.
Another type of resealable vent for dry cells consists of a metal ball overlying a vent opening and biased into sealing engagement around the vent opening by means of a coil spring. The vent opens to release gas from inside the cell when the internal gas pressure reaches a predetermined limit as set by the coil spring. Once the internal gas pressure has been relieved, the coil spring causes the ball to reseat and to reseal the vent.
Another type of resealable vent is disclosed in U.S. Pat. No. 3,415,690 to Richman issued on Dec. 10, 1968. In this vent, a flat elastomeric seal gasket overlies the vent opening and is retained in place by a resilient terminal cap on the top of the cell. This vent operates in basically the same manner as the vents previously described.
In U.S. Pat. No. 3,664,878 to Amthor issued on May 23, 1972, a resealable vent is disclosed which comprises a resilient deformable ball of elastomeric material positioned to overlie a vent orifice provided within the cell's container. A retainer means is positioned over the resilient ball for maintaining the ball in place over the vent orifice and in contact with a valve seat provided around the peripheral edge portions of the vent orifice and for compressing and deforming the resilient ball into a flattened configuration forming a normally fluid-tight seal between the flattened ball and the valve seat. The resilient ball is capable of undergoing further temporary deformation upon the buildup of predetermined high internal gas pressure inside the container so as to momentarily break the seal and allow gas to escape through the vent orifice.
A major problem encountered with resealable pressure relief vent valves of the types just described is that they are bulky and/or difficult to incorporate into the cell assembly. Furthermore, these pressure relief vent valves are expensive to manufacture and most are not adaptable for incorporation into miniature size cells. In addition, some of the prior art resealable vents as exemplified by the foregoing patents are not suitable for low pressure venting.
It is, therefore, an important object of this invention to provide a compact and economical low pressure resealable flapper vent valve for use in a galvanic dry cell.
Still another object of this invention is to provide a resealable flapper vent valve for galvanic dry cells which comprises a cup-shaped washer which is easy to assemble and inexpensive to manufacture.
Another object of this invention is to provide a resealable flapper vent valve that is adaptable to various diameters of drawn or extruded cell containers.
Another object of this invention is to provide a resilient cup-shaped washer as a vent subseal member for galvanic dry cells.
The foregoing and additional objects will become more fully apparent from the following description and the accompanying drawings.